Modulation of the kinetics of cholesterol side-chain cleavage by an activator and by an inhibitor isolated from the cytosol of the cortex of bovine adrenals.

Two modulators of sterol side-chain cleavage activity have been detected in the cytosol from the cortex of bovine adrenals. One is an inhibitor of side-chain cleavage which increases the Km of a purified and reconstituted mitochondrial side-chain cleavage system for both cholesterol and cholesterol sulfate. It also lowers the Vmax of cleavage when cholesterol sulfate is the substrate. The other modulator is a low molecular weight protein which in the reconstituted system increases the Vmax of cleavage for both substrates but does not affect the Km of either. Side-chain cleavage activity was also found in bovine adrenocortical cytosol and this appears to differ from that present in mitochondria.